Lubricating oil composition

ABSTRACT

Lubricating oil composition containing components (A)-(C) in a base oil is provided. The components (A)-(C) are (A) one or more metal detergents selected from optionally substituted divalent metal phenates, optionally substituted divalent metal salts of salicylic acid and optionally substituted divalent metal salts of sulphonic acid; (B) one or more zinc dialkyl dithiophosphates; and (C) one or more compounds selected from (i) one or more fatty acid esters, and/or (ii) one or more further phosphorus compounds.

FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition. More particularly, it relates to a lubricating oil composition that can be used as hydraulic fluid, transmission oil, gear oil and engine oil for diesel, gasoline and gas engines.

BACKGROUND OF THE INVENTION

Lubricating oil compositions such as hydraulic fluids, gear oils, automobile automatic and manual transmission oils and engine oils are typically made by incorporating additives such as corrosion inhibitors and oxidation inhibitors into base oils such as mineral oils or synthetic oils.

As such lubricating oil compositions are used for long periods, resistance to heat and oxidation is essential. Furthermore it is also essential that such lubricating oil compositions are not corrosive to metals.

When a lubricating oil composition degrades, it causes wear of the metal parts being lubricated owing to the decline in its lubricating properties. Such degradation can also give rise to problems by forming sludges which may cause obstruction of hydraulic circuits.

Whilst lubricating oil compositions comprising zinc dialkyl dithiophosphate can be effective in preventing metal wear, sludges can readily form in such lubricating oil compositions because of thermal or oxidative degradation. Thus measures must be taken to prevent such problems.

Furthermore, because of the recent trend towards high performance and compactness in hydraulic devices, transmissions and the like, the conditions of use of lubricating oil compositions have become more severe in terms of high temperatures and high pressures. Hence, there has been a demand for improvements in the performance of such lubricating oil compositions with regard to heat and oxidation as compared with previous lubricating oil compositions.

Unexamined Japanese patent application No. 5-311187 describes heat resistant hydraulic fluid compositions which contain (A) a base oil having a sulphur content of 100 ppm or less, (B) 0.2 to 1 weight % of zinc dithiophosphate, (C) 0.2 to 1 weight % of an alkaline earth metal salt of salicylic acid and (D) 0.01 to 0.5 weight % of a water separating agent, based on the total composition weight.

Unexamined Japanese patent application No. 11-189781 describes lubricating oil compositions which comprise 0.005 to 0.3 weight parts as zinc of a zinc compound of dithiophosphoric acid having two hydrocarbon groups, 0.1 to 3 weight parts of a phosphorus type oxidation inhibitor, 0.1 to 2 weight parts of thiophosphate having 3 hydrocarbon groups and 0.1 to 2 weight parts of a dispersant, per 100 weight parts of a mineral oil and/or synthetic oil lubricating oil base oil.

SUMMARY OF THE INVENTION

A lubricating oil composition is provided comprising:

-   (a) a base oil comprising mineral oil, synthetic oil or mixtures     thereof, -   (b) at least one metal detergent selected from the group consisting     of divalent metal phenates, divalent metal salts of salicylic acid,     and divalent metal salts of sulphonic acid; -   (c) at least one zinc dialkyl dithiophosphates; and -   (d) at least one compound selected from the group consisting of     -   (i) one or more fatty acid esters, and/or     -   (ii) one or more further phosphorus compounds.

DETAILED DESCRIPTION OF THE INVENTION

There has now been found in the present invention, lubricating oil compositions having advantageous properties.

It is desirable to provide lubricating oil compositions which have excellent oxidation inhibiting properties and thermal stability, which prevent the formation of sludge, and which can be used as hydraulic fluids, transmission oils, gear oils and engine oils (for diesel, gasoline and gas engines), which have low viscosity, and excellent fuel economy properties, antiwear properties and antiseize properties.

Accordingly, lubricating oil composition is prepared by blending into a base oil comprising mineral oil, synthetic oil or mixtures thereof,

-   (A) one or more metal detergents selected from optionally     substituted divalent metal phenates, optionally substituted divalent     metal salts of salicylic acid and optionally substituted divalent     metal salts of sulphonic acid; -   (B) one or more zinc dialkyl dithiophosphates; and -   (C) one or more compounds selected from the group of     -   (i) one or more fatty acid esters, and/or     -   (ii) one or more further phosphorus compounds.

That is to say, in one embodiment of the present invention, there is provided a lubricating oil composition comprising a base oil comprising mineral oil, synthetic oil or mixtures thereof,

-   (A) one or more metal detergents selected from optionally     substituted divalent metal phenates, optionally substituted divalent     metal salts of salicylic acid and optionally substituted divalent     metal salts of sulphonic acid; -   (B) one or more zinc dialkyl dithiophosphates; and -   (C) (i) one or more fatty acid esters.

Another embodiment of the present invention provides a lubricating oil composition comprising a base oil comprising mineral oil, synthetic oil or mixtures thereof,

-   (A) one or more metal detergents selected from optionally     substituted divalent metal phenates, optionally substituted divalent     metal salts of salicylic acid and optionally substituted divalent     metal salts of sulphonic acid; -   (B) one or more zinc dialkyl dithiophosphates; and -   (C) (ii) one or more further phosphorus compounds.

In a further embodiment of the present invention, there is provided a lubricating oil composition comprising a base oil comprising mineral oil, synthetic oil or mixtures thereof,

-   (A) one or more metal detergents selected from optionally     substituted divalent metal phenates, optionally substituted divalent     metal salts of salicylic acid and optionally substituted divalent     metal salts of sulphonic acid; -   (B) one or more zinc dialkyl dithiophosphates; -   (C)     -   (i) one or more fatty acid esters; and     -   (ii) one or more further phosphorus compounds.

The base oil used in the lubricating oil compositions in the present invention may comprise any mineral oil, any synthetic oil or mixtures thereof.

Base oils of mineral origin may include those produced by solvent refining or hydroprocessing.

Mineral oils that may be conveniently used include paraffinic oils or naphthenic oils or normal paraffins, for example, those produced by refining lubricating oil cuts obtained by low pressure distillation of atmospheric residual oils which were in turn obtained by atmospheric distillation of crude oil.

Examples of mineral oils that may conveniently be used include those sold by member companies of the Royal Dutch/Shell Group under the designations “HVI”, “MVIN”, or “HMVIP”.

Specific examples of synthetic oils that may be conveniently used include polyolefins such as poly-α-olefins, co-oligomers of ethylene and α-olefins and polybutenes, poly(alkylene glycol)s such as poly(ethylene glycol) and poly(propylene glycol), diesters such as di-2-ethylhexyl sebacate and di-2-ethylhexyl adipate, polyol esters such as trimethylolpropane esters and pentaerythritol esters, perfluoroalkyl ethers, silicone oils and polyphenyl ethers. Such synthetic oils may be conveniently used as single oils or as mixed oils.

Base oils of the type manufactured by the hydroisomerisation of wax, such as those sold by member companies of the Royal Dutch/Shell Group under the designation “XHVI” (trade mark), may also be used.

In the present invention, the phrase “optionally substituted” is used to describe divalent metal phenates, divalent metal salts of salicylic acid and divalent metal salts optionally containing one or more alkyl group substituents.

With regard to component (A), such one or more metal detergents selected from optionally substituted divalent metal phenates, optionally substituted divalent metal salts of salicylic acid and optionally substituted divalent metal salts of sulphonic acid are preferably incorporated in the lubricating oil compositions of the present invention in a total amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.

In a preferred embodiment of the present invention, the lubricating oil compositions as described herein comprise one or more metal detergents (A) which are divalent metal salts of salicylic acid having one or more alkyl group substituents.

The lubricating oil compositions of the present invention preferably comprise basic divalent metal detergents as component (A). Basic calcium detergents are particularly preferable.

Such basic divalent detergents and, in particular, basic calcium detergents are especially effective in preventing synchroniser ring wear.

Whilst the one or more zinc dialkyl dithiophosphates used as component (B) in the lubricating oil compositions of the present invention, have synchroniser ring wear inhibiting properties even when used alone, it has been surprisingly found in the present invention that the simultaneous use thereof with one or more metal detergents used as component (A) gives rise to enhanced effects.

The total base number of basic divalent metal detergents for use as component (A) is preferably in the range of from 50 to 350 mg KOH/g. The divalent metal phenates may be substituted. The divalent metal salts of salicylic acid may be substituted. The divalent metal salts of sulphonic acid may be substituted. Such substituent are suitably groups inert in the lubricant composition such as, for example, alkyl groups.

If the total base number of such basic divalent metal detergents is less than 50 mg KOH/g, then the wear inhibiting properties of the lubricating oil composition may not be observed. On the other hand, if the total base number of such basic divalent metal detergents exceeds 350 mg KOH/g, then there may be the risk of inhibiting the action of other additives in such a lubricating oil composition.

As specific examples of component (A), one or more basic metal detergents selected from (A-1) calcium sulphonates having a total base number in the range of from 50 to 350 mg KOH/g, (A-2) calcium phenates having a total base number in the range of from 50 to 350 mg KOH/g and (A-3) calcium salicylates having a total base number in the range of from 50 to 350 mg KOH/g, may be conveniently used in the lubricating oil compositions of the present invention.

Examples of calcium sulphonates that may be conveniently used include calcium salts of alkylaromatic sulphonic acids obtained by sulphonation of alkylaromatic compounds of molecular weight in the range of from 100 to 1500. Alkylaromatic sulphonic acids that may be conveniently used to produce such salts include so-called petroleum sulphonic acids and synthetic sulphonic acids.

Examples of calcium phenates that may be conveniently used include calcium salts of alkylphenols having at least one linear or branched 4 to 30 carbon alkyl group, calcium salts of alkylphenol sulphides obtained by reacting the afore-mentioned alkylphenols with elemental sulphur or calcium salts of alkylphenol Mannich reaction products obtained by reacting the afore-mentioned alkylphenols and formaldehyde.

Examples of calcium salicylates that may be conveniently used include calcium salts of alkylsalicylic acids having at least one linear or branched 4 to 30 carbon alkyl group.

In the lubricating oil compositions of the present invention, if two or more metal detergents are used as component (A) simultaneously, then the total amount of such metal detergents in the lubricating oil compositions of the present invention is preferably in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.

If the amount of component (A) in the lubricating oil compositions of the present invention is less than 0.3 weight %, per 100 weight % of lubricating oil composition, then the synchroniser ring wear inhibition improving properties of the lubricating oil composition due to the simultaneous use of component (A) may be poor. On the other hand, if the amount of component (A) in the lubricating oil compositions of the present invention exceeds 5.0 weight %, then this may be undesirable as the quantity of sludge and the like formed when the lubricating oil compositions degrade may increase.

With regard to component (B), such one or more zinc dialkyl dithiophosphates are preferably incorporated in the lubricating oil compositions of the present invention in a total amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.

The total amount of such one or more zinc dialkyl dithiophosphates (B) in the lubricating oil compositions of the present invention is more preferably in the range of from 0.5 to 3.0 weight %.

If the total amount of such one or more zinc dialkyl dithiophosphates (B) is less than 0.3 weight %, then the wear-decreasing effect may not be seen, and there is a risk that the amount of wear will increase. If the total amount of such one or more zinc dialkyl dithiophosphates (B) exceeds 5.0 weight %, then there may be no further wear reducing effect and there is a risk that in a high temperature use environment oxidative degradation products may increase.

Examples of alkyl groups that may be conveniently employed in such one or more zinc dialkyldithiophosphates (B) include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, and octadecyl group.

The one or more fatty acid esters (C)(i) are preferably incorporated in the lubricating oil compositions of the present invention in a total amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.

The total amount of such one or more fatty acid esters (C) (i) in the lubricating oil compositions of the present invention is more preferably in the range of from 0.5 to 3.0 weight %, per 100 weight % of lubricating oil composition.

If the amount of such one or more fatty acid esters (C) (i) is less than 0.3 weight %, then the wear-decreasing effect may not be seen, and there is a risk that the anti-seize properties may be decreased. If the amount of such one or more fatty acid esters (C) (i) exceeds 5.0 weight %, then there may be no further efficacy, and, depending on the circumstances, there may be a risk of impairing the action of other additives, and of decreasing the wear inhibition and anti-seize properties.

Examples of fatty acids which may be conveniently used in the manufacture of the one or more fatty acid esters (C) (i) include linear or branched saturated fatty acids such as heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, eicosanoic acid, heneicosanoic acid, docosanoic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoic acid and triacontanoic acid; linear or branched unsaturated fatty acids (the position of the double bond(s) is not limited) such as heptenoic acid, octenoic acid, nonenoic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, heptadecenoic acid, octadecenoic acid, nonadecenoic acid, eicosenoic acid, heneicosenoic acid, docosenoic acid, tricosenoic acid, tetracosenoic acid, pentacosenoic acid, hexacosenoic acid, heptacosenoic acid, octacosenoic acid, nonacosenoic acid and triacontenoic acid.

As the one or more fatty acid esters (C) (i), esters of polyhydric alcohols with the aforesaid fatty acids are preferred.

Polyhydric alcohols may conveniently be 3 to 6 carbon polyhydric alcohols or dimers and trimers thereof, and, specifically, polyhydric alcohols such as glycerine, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitan, diglycerine, ditrimethylolethane, di-trimethylolpropane, dipentaerythritol, triglycerine, tritrimethylolethane, tritrimethylolpropane, tripentaerythritol and dimers and trimers thereof.

Such esters of polyhydric alcohols may be either so-called fully esterified substances wherein all the hydroxyl groups in the polyhydric alcohol are esterified or so-called partially esterified substances, wherein at least one hydroxyl group in the polyhydric alcohol is not esterified and still remains in hydroxyl group form.

A particularly preferred fatty acid ester (C) (i) is glycerine monooleate.

The lubricating oil compositions of the present invention preferably comprise further phosphorus compounds (C) (ii) (in addition to the one or more zinc dialkyldithiophosphates (B)).

Through the simultaneous use of one or more further phosphorus compounds (C) (ii), there is further improvement of the wear inhibiting properties of the lubricating oil compositions of the present invention.

With regard to component (C) (ii), such one or more further phosphorus compounds are preferably incorporated in the lubricating oil compositions of the present invention, in a total amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.

Examples of the one or more further phosphorus compounds of component (C) (ii) that may be conveniently used in the lubricating oil compositions of the present invention include one or more compounds selected from phosphate esters and derivatives thereof, phosphite esters and derivatives thereof.

Particularly preferred further phosphorus compounds (C) (ii) that may be conveniently used in the lubricating oil compositions of the present invention include one or more compounds selected from monoalkyl phosphates and monoalkyl thiophosphates (the alkyl groups in such phosphates and thiophosphates may be linear or branched) such as monobutyl phosphate, monopentyl phosphate, monohexyl phosphate, monoheptyl phosphate, monooctyl phosphate, monononyl phosphate, monodecyl phosphate, monoundecyl phosphate, monododecyl phosphate, monotridecyl phosphate, monotetradecyl phosphate, monopentadecyl phosphate, monohexadecyl phosphate, monoheptadecyl phosphate, monooctadecyl phosphate, monononadecyl phosphate, monoeicosyl phosphate, monoheneicosyl phosphate, monodocosyl phosphate, monotricosyl phosphate and monotetracosyl phosphate; monoalkenyl phosphates and monoalkenyl thiophosphates (the alkenyl groups in such phosphates and thiophosphates may be linear or branched) such as monooctadecenyl phosphate; mono(alkyl)aryl phosphates and mono(alkyl)aryl thiophosphates (the alkyl groups in such phosphates and thiophosphates may be linear or branched) such as monophenyl phosphate and monocresyl phosphate; dialkyl phosphates and dialkyl thiophosphates (the alkyl groups in such phosphates and thiophosphates may be linear or branched) such as dibutyl phosphate, dipentyl phosphate, dihexyl phosphate, diheptyl phosphate, dioctyl phosphate, dinonyl phosphate, didecyl phosphate, diundecyl phosphate, didodecyl phosphate, ditridecyl phosphate, ditetradecyl phosphate, dipentadecyl phosphate, dihexadecyl phosphate, diheptadecyl phosphate, dioctadecyl phosphate, dinonadecyl phosphate, dieicosyl phosphate, diheneicosyl phosphate, didocosyl phosphate, ditricosyl phosphate and ditetracosyl phosphate; dialkenyl phosphates and dialkenyl dithiophosphates (the alkenyl groups in such phosphates or thiophosphates may be linear or branched) such as dioctadecenyl phosphate; di(alkyl)aryl phosphates and di(alkyl)aryl thiophosphates (the alkyl groups in such phosphates and thiophosphates may be linear or branched) such as diphenyl phosphate and dicresyl phosphate; monoalkyl phosphites and monoalkyl thiophosphites (the alkyl group in such phosphites and thiophosphites may be linear or branched) such as monobutyl phosphite, monopentyl phosphite, monohexyl phosphite, monoheptyl phosphite, monooctyl phosphite, monononyl phosphite, monodecyl phosphite, monoundecyl phosphite, monododecyl phosphite, monotridecyl phosphite, monotetradecyl phosphite, monopentadecyl phosphite, monohexadecyl phosphite, mono-heptadecyl phosphite, monooctadecyl phosphite, monononadecyl phosphite, monoeicosyl phosphite, monoheneicosyl phosphite, monodocosyl phosphite, monotricosyl phosphite and monotetracosyl phosphite; monoalkenyl phosphites and monoalkenyl thiophosphites (the alkenyl groups in such phosphites and thiophosphites may be linear or branched) such as monooctadecenyl phosphite; mono(alkyl)aryl phosphites and mono(alkyl)aryl thiophosphites (the alkyl groups in such phosphites and thiophosphites may be linear or branched) such as monophenyl phosphite and monocresyl phosphite; dialkyl phosphites and dialkyl thiophosphites (the alkyl groups in such phosphites and thiophosphites may be linear or branched) such as dibutyl phosphite, dipentyl phosphite, dihexyl phosphite, diheptyl phosphite, dioctyl phosphite, dinonyl phosphite, didecyl phosphite, diundecyl phosphite, didodecyl phosphite, ditridecyl phosphite, ditetradecyl phosphite, dipentadecyl phosphite, dihexadecyl phosphite, diheptadecyl phosphite, dioctadecyl phosphite, dinonadecyl phosphite, dieicosyl phosphite, diheneicosyl phosphite, didocosyl phosphite, ditricosyl phosphite and ditetracosyl phosphite; dialkenyl phosphites and dialkenyl thiophosphites (the alkenyl groups in such phosphites and thiophosphites may be linear or branched) such as dioctadecenyl phosphite; di(alkyl)aryl phosphites and di(alkyl)aryl thiophosphites (the alkyl groups in such phosphites thiophosphites may be linear or branched) such as diphenyl phosphite and dicresyl phosphite.

Salts of the afore-mentioned phosphorus compounds (C) (ii) with amines and alkanolamines; or mixtures thereof may also be conveniently used in the lubricating oil compositions of the present invention.

In the lubricating oil compositions of the present invention, if component (C) (ii) is used therein, then the total amount of such one or more further phosphorus compounds is more preferably in the range of from 0.5 to 3.0 weight %, per 100 weight % of lubricating oil composition.

If the amount of component (C) (ii) in such lubricating oil compositions is less than 0.3 weight % then its effects on the wear inhibition properties may not be seen. If the amount of component (C) (ii) in such lubricating oil compositions exceeds 5.0 weight % then there may be a risk that the corrosion properties and antifoam properties of the lubricating oil compositions will worsen.

Moreover, as necessary in order further to improve their properties, the lubricating oil compositions of the present invention may also contain optional amounts of additional additives such as extreme pressure agents such as sulphurised oils or fats, antioxidants, anticorrosive agents and antifoam agents such as dimethylsilicones.

In a preferred embodiment of the present invention, the lubricating oil compositions as described herein are characterised in that they have oxidation stability such that, in a test based on the JIS K 2514 ISOT test, the increase in acid value after 96 hours at 135° C. is 0.50 mg KOH/g or less.

JIS K 2514, the internal combustion engine lubricating oil oxidation stability test (ISOT test), is a test which was originally developed as a method for assessment of the thermal stability of internal combustion engine lubricating oils. However, at present it is also widely used for the assessment of gear oils and the like.

A special beaker into which iron and copper catalysts had been introduced is placed in a temperature-controlled oil bath of the lubricating oil composition to be tested. Oxidative degradation is accelerated with entrainment of air by stirring for a specified number of revolutions.

After the test, the extent of degradation of the lubricating oil composition is investigated by measuring the viscosity, acid value and base value thereof and the amount of sludge that has been formed. In particular, the acid value decreases somewhat in the early stages owing to consumption of the additives, and then abruptly increases when the acid neutralising action of any basic metal detergents present therein decreases as degradation of the lubricating oil composition accelerates.

If the increase in acid value after 96 hours is 0.50 mg KOH/g or less, then there is no problem. However, if the increase in acid value exceeds this value, then there is a high probability that the acid value will increase abruptly.

Concerning the synchroniser frictional properties test and the wear properties test, in manual transmission gear change mechanisms, a synchromesh mechanism is used so as simultaneously to mesh pairs of gears with different rotation speeds. The synchroniser rings and gear cones which are the main structural elements of this simultaneous meshing mechanism come into contact through being forcibly thrust together during a gear change, and as a result of the difference in revolution rates being brought to zero by the frictional forces produced, the meshing of the gears can be effected, completing the gear change.

In this case, if the frictional force between the synchroniser rings and gear cones is small, then proper synchronisation does not take place, the two gears come into contact with different rotation speeds, and noise and gear damage may occur. Hence, it is essential that with the lubricating oil composition used, the coefficient of friction between the synchroniser ring and gear cone is no less than a certain value.

In another preferred embodiment of the present invention, the lubricating oil compositions as described herein are characterised in that, among the synchroniser properties, the coefficient of friction is 0.100 or more.

The inside of the synchroniser ring and the outside of the gear cone come into contact, but normally, in order to increase the coefficient of friction of the inside of the synchroniser ring, a large number of grooves are cut in the slide direction. If the antiwear properties of the lubricating oil composition used are poor, then the projections in this grooved area can become worn and deformed, affecting the coefficient of friction, and there is a risk that in some cases synchronisation will be impossible. Hence, the lubricating oil used must have such synchroniser antiwear properties.

In another preferred embodiment of the present invention, the lubricating oil compositions as described herein are characterised in that, among the synchroniser properties, the amount of wear is 0.60 mm or less.

By means of the present invention, it has been surprisingly possible to provide lubricating oil compositions which have excellent antioxidant properties and thermal stability, which prevent sludge formation, which have low viscosity, excellent fuel economy properties, antiwear properties and anti-seize properties and which can be conveniently used as hydraulic fluids, transmission oils, gear oils and engine oils (diesel, gasoline and gas) and the like.

Accordingly, the present invention further provides methods of lubricating hydraulic systems, gears, engines (diesel, gasoline and gas) and manual and automatic transmission systems using the lubricating oil compositions of the present invention.

The present invention further provides the use of the lubricating oil compositions of the present invention in order to reduce sludge formation and/or as anti-wear lubricating oil compositions, in particular the use of such lubricating oil compositions to reduce sludge formation and/or as anti-wear lubricating oil compositions in a manual transmission system.

The lubricating oil compositions of the present invention may be conveniently prepared by incorporating into a base oil comprising mineral oil, synthetic oil or mixtures thereof,

-   (A) one or more metal detergents selected from optionally     substituted divalent metal phenates, optionally substituted divalent     metal salts of salicylic acid and optionally substituted divalent     metal salts of sulphonic acid; -   (B) one or more zinc dialkyl dithiophosphates; and -   (C) one or more compounds selected from the group of     -   (i) one or more fatty acid esters, and/or     -   (ii) one or more further phosphorus compounds,         in conjunction with any additional additives that are desired         therein.

The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way.

EXAMPLES Examples and Comparative Examples

In Tables 1 to 3, the numerical values for each component show the weight % of each component, and “rem.” shows the remainder of purified mineral oil base oil, taking the total amount of the lubricating oil composition as 100 weight %.

In Tables 1 to 3:

-   (1) “Ca salicylate” means: Ca salicylate of total base number 170 mg     KOH/g, -   (2) “Ca sulphonate” means: Ca sulphonate of total base number 300 mg     KOH/g, -   (3) “Ca phenate” means: Ca phenate of total base number 250 mg     KOH/g, -   (4) “Purified mineral oil” means: paraffinic mineral oil (kinematic     viscosity at 100° C. 5.2 mm²/sec, viscosity index 105), -   (5) “Phosphorus compound” means: didodecyl phosphite, -   (6) “Fatty acid ester” means: glycerine monooleate, -   (7) “ZnDTP” means: primary type zinc dialkyl dithiophosphate having     eight-carbon alkyl groups, and -   (8) “Antioxidant A” means: 2,6-di-tert-butyl-4-methylphenol.

The ISOT test for oxidation stability, synchroniser friction test and synchroniser wear test were performed on the lubricating oil compositions described in Tables 1 to 3.

The test results are shown in Table 1 (Examples) and Tables 2 and 3 (Comparative Examples).

The methods described below were used for the respective tests.

1. Oxidation Stability

The assessment of oxidation stability was performed in accordance with JIS K 2514, the internal combustion engine lubricating oil oxidation stability test (ISOT, Indiana Stirring Oxidation Test).

The acid numbers of the fresh oil (the lubricating oil composition used in the test) and degraded oil (the same lubricating oil composition after the test) were measured in accordance with JIS K 2501.

Those lubricating oil compositions wherein the increase in acid number was 0.50 mg KOH/g or less were scored as a pass (◯), and those wherein it exceeded 0.50 mg KOH/g were scored as a fail (X).

Test Conditions

-   Test temperature: 135° C., Test period: 96 hours     2. Synchroniser Friction Properties

The method for assessment of the synchroniser friction properties was implemented under the following test conditions, using a synchroniser test machine.

Coefficients of friction of 0.100 or more were scored as a pass (◯), and those coefficients of friction of less than 0.100 were scored as a fail (X).

Test Conditions

-   Test pieces: copper alloy synchroniser rings, steel gear cones -   Test oil temperature: 80° C., Load: 400 N, Slide rate: 5 m/sec, -   Number of test cycles: 100 000 cycles (1 cycle: 0.5 secs ON, 1.0 sec     OFF)     3. Synchroniser Wear Properties

The method for assessment of the synchroniser wear properties was implemented under the following test conditions, using a synchroniser test machine. Those where the amount of wear (change in gap between synchroniser ring and gear cone) was 0.60 mm or less were scored as a pass (◯), and those where it exceeded 0.60 mm were scored as a fail (X)

Test Conditions

-   Test pieces: copper alloy synchroniser rings, steel gear cones -   Test oil temperature: 80° C., Load: 400 N, Slide rate: 5 m/sec,

Number of test cycles: 100 000 cycles (1 cycle: 0.5 secs ON, 1.0 sec OFF) TABLE 1 Examples 1 2 3 4 5 6 7 8 (A) Ca salicylate, wt. % 1.4 1.4 1.4 1.4 0.7 0.7 Ca sulphonate, wt. % 0.7 1.4 Ca phenate, wt. % 1.4 0.7 (B) ZnDTP, wt. % 0.8 0.8 0.8 1.5 0.8 0.8 0.8 0.8 (C)(i) Fatty acid ester, wt. % 0.3 0.3 0.3 0.3 0.3 0.3 (C)(ii) Phosphorus compound, wt. % 0.6 0.6 1.2 0.6 0.6 0.6 0.6 Antioxidant A, wt. % 0.3 0.3 purified mineral oil, wt. % rem. rem. rem. rem. rem. rem. rem. rem. Oxidation stability, ISOT ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ test, increase in acid 0.3 0.4 0.4 0.2 0.3 0.4 0.4 0.3 value (mg KOH/g) Synchroniser properties, ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ coefficient of friction 0.11 0.12 0.12 0.14 0.12 0.12 0.13 0.13 Synchroniser properties, ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ amount of wear 0.4 0.5 0.6 0.4 0.3 0.5 0.5 0.4 (mm)

TABLE 2 Comparative Examples 1 2 3 4 5 6 7 8 (A) Ca salicylate, wt. % 1.4 Ca sulphonate, wt. % 1.4 Ca phenate, wt. % 1.4 (B) ZnDTP, wt. % 0.8 (C) (i) Fatty acid ester, wt. % 0.8 (C) (ii) Phosphorus compound, wt. % 0.6 Antioxidant A, wt. % 0.3 Purified mineral oil, wt. % 100.0 rem. rem. rem. rem. rem. rem. rem. Oxidation stability, ISOT X X X X X ◯ X X test, increase in acid 3.2 1.2 1.8 2.2 0.8 0.5 1.3 1.2 value (mg KOH/g) Synchroniser properties, X X X X ◯ X X X coefficient of friction 0.05 0.09 0.08 0.08 0.11 0.06 0.08 0.09 Synchroniser properties, X X X X ◯ X X X amount of wear 1.2 0.9 0.7 1.0 0.5 1.1 0.9 1.0 (mm)

TABLE 3 Comparative Examples 9 10 11 12 13 14 15 16 17 18 (A) Ca salicylate, wt. % 1.4 1.4 Ca sulphonate, wt. % 1.4 Ca phenate, wt. % 1.4 (B) ZnDTP, wt. % 0.8 0.8 0.8 0.8 (C) (a) Fatty acid ester, wt. % 0.8 0.8 0.8 0.8 (C) (ii) Phosphorus compound, 0.6 0.6 0.6 0.6 wt. % Antioxidant A, wt. % 0.3 0.3 0.3 0.3 Purified mineral oil, rem. rem. rem. rem. rem. rem. rem. rem. rem. rem. wt. % Oxidation stability, X X ◯ ◯ X X X X X ◯ ISOT test, increase in 1.4 1.5 0.5 0.4 2.1 1.2 1.0 1.5 1.0 0.4 acid value (mg KOH/g) Synchroniser properties, X X ◯ X X X X X X X coefficient of friction 0.08 0.08 0.13 0.09 0.08 0.09 0.08 0.09 0.08 0.08 Synchroniser properties, X X X X X X X X X X amount of wear 0.8 0.9 0.7 1.1 0.8 0.7 0.8 0.9 1.0 0.7 (mm)

From these Examples and Comparative Examples, it is apparent that in the Examples according to the present invention, through the incorporation of 3 types of additive (A), (B), (C), which are essential components in the present invention, lubricating oil compositions with good oxidation stability, frictional properties and wear properties are surprisingly obtained.

On the other hand, from such Examples and Comparative Examples, it is also apparent that the lubricating oil compositions of Comparative Examples 1 to 18, wherein the 3 types of additive (A), (B), (C) which are essential components in the present invention, were not all incorporated, did not meet the target values. 

1. A lubricating oil composition comprising: (a) a base oil comprising mineral oil, synthetic oil or mixtures thereof, (b) at least one metal detergent selected from the group consisting of divalent metal phenates, divalent metal salts of salicylic acid, and divalent metal salts of sulphonic acid; (c) at least one zinc dialkyl dithiophosphates; and (d) at least one compound selected from the group consisting of (i) one or more fatty acid esters, and/or (ii) one or more further phosphorus compounds.
 2. The lubricating oil composition of claim 1 wherein component d) is at least one fatty acid ester.
 3. The lubricating oil composition of claim 1 wherein component d) is at least one further phosphorus compound.
 4. The lubricating oil composition of claim 1 wherein component d) comprise i) at least one fatty acid ester; and ii) at least one further phosphorus compound.
 5. The lubricating oil composition of claim 1 wherein the metal detergent component b) is present in a total amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.
 6. The lubricating oil composition of claim 1 wherein the zinc dialkyl dithiophosphates component c) is present in a total amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.
 7. The lubricating oil composition of claim 4 wherein the components (d)(i) and (d)(ii) are each present in an amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.
 8. The lubricating oil composition of claim 1 wherein it has oxidation stability such that, in a test based on the JIS K 2514 ISOT test, the increase in acid value after 96 hours at 135° C. is 0.50 mg KOH/g or less.
 9. The lubricating oil composition of claim 1 wherein among the synchroniser properties, the coefficient of friction is 0.100 or more and/or the amount of wear is 0.60 mm or less.
 10. The lubricating oil composition of claim 1 wherein the metal detergent component b) is divalent metal salt of salicylic acid having one or more alkyl group substituents.
 11. The lubricating oil composition of claim 1 wherein the metal detergent component b) is a calcium salt of alkylphenols having at least one linear or branched 4 to 30 carbon alkyl group or calcium salts of alkylphenol sulphides.
 12. The lubricating oil composition of claim 1 wherein the metal detergent component b) is a calcium salt of alkylaromatic sulphonic acid.
 13. The lubricating oil composition of claim 1 wherein the component (d) is present in an amount in the range of from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition.
 14. A lubricating oil composition comprising: (a) a base oil comprising mineral oil, synthetic oil or mixtures thereof, (b) from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition, of at least one metal detergent selected from the group consisting of divalent metal phenates, divalent metal salts of salicylic acid, and divalent metal salts of sulphonic acid; (c) from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition, of at least one zinc dialkyl dithiophosphates; and (d) from 0.3 to 5.0 weight %, per 100 weight % of lubricating oil composition, of at least one compound selected from the group consisting of (i) one or more fatty acid esters, and/or (ii) one or more further phosphorus compounds. 